Plant pests are a major factor for the loss of crops, resulting in tremendous economic loss of farmers and even affecting the living conditions of local people. Broad-spectrum chemical insecticides and biotic insecticides are often used by people to prevent and control plant pests. However, there are limits for them to be used in practical application: chemical insecticides will lead to environmental contamination and the appearance of drug-resistant insects; and biotic insecticides are easily degraded in environment and need to be applied repeatedly during production, which dramatically increases the production cost.
To address the limitations of chemical insecticides and biotic insecticides in practical application, scientists have found, based on researches, that some insect-resistant transgenic plants can be obtained by transferring insect-resistant gene of encoding insecticidal protein into plants, to prevent and control plant pests. PIC9 insecticidal protein is one of the insecticidal proteins, produced by Bacillus thuringiensis sbusp. kurstaki, B.t.k. PIC9 is a parasporal insoluble crystal protein.
PIC9 protein is ingested into the mesenteron of insects, and the toxalbumin protoxin is dissolved in alkaline pH environment of insect mesenteron. Protein N-terminal and C-terminal are digested by alkaline proteinase and the protoxin is converted into active fragments. These active fragments are bounded to receptors on the upper surface of epithelial membrane of insect mesenteron, and inserted into the intestine membrane, which results in cell membrane perforation lesions, destroy of the change of osmotic pressure and the pH balance inside and outside cell membrane, and disturbance of the digestion process of insects and finally leading to their death.
There is severe grain loss every year by plant pests, such as maize borer, agrotis ypsilon, maize armyworm, or cotton bollworm. So far, there are no reports about the expression level and toxicity of PIC9 insecticidal protein in plants.